The present invention relates to snow skis and, more specifically, to skis having adjustable camber-flattening resistance and a method for providing cambered skis having a desired camber-flattening resistance.
The present invention is particularly useful in cross country skis because of the extreme importance of the ski camber, or, more particularly, the camber-flattening resistance of cross country skis to their satisfactory performance. A cross country ski must slide smoothly and freely on the snow in the glide mode, that is, when no driving force is exerted on it by the skier, but must provide significant frictional engagement with the snow during the kick mode, that is, when downward driving force is applied. The ski camber and camber-flattening resistance are important factors in performance.
Such dual functioning is achieved, of course, by the alternate flattening and arching of the ski as it changes from glide mode to kick mode and back again. The most commonly used cross-country skiing technique is the diagonal stride technique. Using this technique, when one ski is in the kick mode, the other is normally in the glide mode, and vice versa. Whatever technique is used, however, in the glide mode the skier's foot is simply resting on the mid-portion of the ski, which has a substantial camber, while in the kick mode the skier exerts a downward, driving force on the ski, which reduces or eliminates the camber.
In the glide mode the ski camber keeps the lower surface of the mid-portion of the ski, that is, the portion generally below the skier's foot, raised above the snow surface or at least prevents loaded contact with the snow. The front and rear portions of the ski, that is, the portions on either side of the mid-portion, bear the weight of the skier in the glide mode.
Such front and rear portions are smooth and are normally waxed to provide good sliding action over the snow. The mid-portion of the lower surface, however, has different surface characteristics, in shape, surface material, and/or a coating (such as "kick wax"), and therefore does not slide as easily over the snow, providing instead a degree of frictional engagement or "bite."
When the ski is in the kick mode, with additional force being applied to the ski mid-portion by the skier's foot, the camber of the ski is flattened to some extent to obtain frictional engagement with the snow. Such frictional engagement allows the skier to thrust his other ski forward in the glide mode. As the skier shuffles along, his left and right skis alternate between the gliding mode and the kick mode.
The camber-flattening resistance of cross country skis is critical to successful operation. If the skis are too rigid, the skier will not be able to engage the mid-portion properly with the snow in the kick mode. On the other hand, if the skis are too flexible, the skier will not glide well in the gliding mode because of the unnecessary friction created between the midportion and the snow.
A number of factors must be considered in choosing an appropriate degree of flexibility. The most obvious of these is the skier's weight. Heavier skiers more easily flatten the ski camber than lighter skiers and usually require a greater camber-flattening resistance in their skis. Another factor is the skier's ability. Highly skilled skiers can exert a great deal more downward driving force than less skilled skiers of the same weight. Thus, highly skilled skiers might prefer a greater camber-flattening resistance in their skis in order to assure good gliding qualities in the gliding mode. Finally, snow conditions are another factor to be considered in choosing a cross country ski. Wet snow tends to allow a better bite than dry snow. Accordingly, a given skier may need skis with a lower camber-flattening resistance for dry snow than he would for wet snow.
In the past, ski manufacturers and sellers have produced a large variety of skis having numerous lengths and flexibilities as a means of providing skis with appropriate camber-flattening resistance for various skiers. While some skiers are able to obtain skis with highly desirable camber-flattening resistance for their weight, skill level, and so forth, many skiers buy skis providing less than optimum performance for them.
Furthermore, over a period of years the skier's weight and his level of ability will change. And, snow conditions obviously change from day to day and hour to hour. A need has existed for a ski which can accommodate widely varying skiers and changing conditions.